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United States Patent |
6,111,544
|
Dakeya
,   et al.
|
August 29, 2000
|
Chip antenna, antenna device, and mobile communication apparatus
Abstract
The invention provides a chip antenna comprising: a substrate made by
laminating a plurality of sheet layers made of ceramic; a radiating
conductor having substantially planar shape and provided on said
substrate; a grounding conductor having substantially planar shape and
provided so as to oppose said radiating conductor with said sheet layers
interposed in between; a capacitor conductor having substantially planar
shape and provided so as to oppose said radiating conductor and said
grounding conductor with said sheet layers interposed in between; a first
shorting conductor which connects said radiating conductor and said
grounding conductor; a second shorting conductor which connects said
grounding conductor and said capacitor conductor; a feed terminal
connected to said radiating conductor or said capacitor conductor; and a
ground terminal connected to said grounding conductor. According to the
above a chip antenna, the resonance frequency can be adjusted readily with
compact size can be achieved.
Inventors:
|
Dakeya; Yujiro (Omihachiman, JP);
Tsuru; Teruhisa (Kameoka, JP);
Kanba; Seiji (Kusatsu, JP);
Suesada; Tsuyoshi (Shiga-ken, JP)
|
Assignee:
|
Murata Manufacturing Co., Ltd. (JP)
|
Appl. No.:
|
245426 |
Filed:
|
February 4, 1999 |
Foreign Application Priority Data
| Feb 13, 1998[JP] | 10-031392 |
| Jul 24, 1998[JP] | 10-209515 |
| Sep 29, 1998[JP] | 10-275831 |
Current U.S. Class: |
343/700MS; 343/702 |
Intern'l Class: |
H01Q 001/38 |
Field of Search: |
343/700 MS,702,846,848
|
References Cited
U.S. Patent Documents
4827266 | May., 1989 | Sato et al. | 343/700.
|
5585810 | Dec., 1996 | Tsuru et al. | 343/700.
|
5767808 | Jun., 1998 | Robbins et al. | 343/846.
|
5898403 | Apr., 1999 | Saitoh et al. | 343/700.
|
5917450 | Jun., 1999 | Tsunekawa et al. | 343/700.
|
Primary Examiner: Ho; Tan
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb & Soffen, LLP
Claims
What is claimed is:
1. A chip antenna, comprising:
a substrate made by laminating a plurality of sheet layers made of ceramic;
a radiating conductor having a substantially planar shape and provided on
said substrate;
a grounding conductor having a substantially planar shape and provided so
as to oppose said radiating conductor with said sheet layers interposed in
between;
a capacitor conductor having a substantially planar shape and provided so
as to oppose said radiating conductor with at least one of said sheet
layers interposed in between;
a first shorting conductor which connects said radiating conductor and said
grounding conductor;
a second shorting conductor which connects said grounding conductor and
said capacitor conductor;
a feed terminal connected to at least one of said radiating conductor and
said capacitor conductor; and
a ground terminal connected to said grounding conductor.
2. The chip antenna according to claim 1, wherein a plurality of said
radiating conductors are provided and at least one of said radiating
conductors is fed.
3. An antenna device, comprising:
the chip antenna according to claim 1 or claim 2; and
a mounting circuit board, having a protruding part extending from the end
part thereof;
said chip antenna being mounted to one of the main surfaces of said
protruding part and there being a ground electrode provided on the other
main surface of said mounting circuit board.
4. Mobile communication apparatus, wherein the antenna device according to
claim 3 is used.
5. An antenna device, comprising:
the chip antenna according to claim 2; and
a mounting circuit board, having a protruding part extending from the end
part thereof;
said chip antenna being mounted to one of the main surfaces of said
protruding part and there being a ground electrode provided on the other
main surface of said mounting circuit board.
6. Mobile communication apparatus, wherein the antenna device according to
claim 4 is used.
7. An antenna device, comprising:
the chip antenna according to claim 2; and
a mounting circuit board having said chip antenna mounted on one of the
main surfaces thereof and having a ground electrode provided on the other
main surface thereof;
said ground electrode having a gap part in the vicinity of the location at
which the chip antenna is mounted.
8. Mobile communication apparatus, wherein the antenna device according to
claim 6 is used.
9. An antenna device, comprising:
the chip antenna according to claim 1; and
a mounting circuit board having said chip antenna mounted on one of the
main surfaces thereof and having a ground electrode provided on the other
main surface thereof;
said ground electrode having a gap part in the vicinity of the location at
which the chip antenna is mounted.
10. Mobile communication apparatus, wherein the antenna device according to
claim 5 is used.
11. The chip antenna according to claim 1, wherein the capacitor conductor
has a capacitance and an area, the capacitance being adjusted by a gap
comprising a thickness of a dielectric layer between the radiating
conductor and the capacitor conductor, and the overlapping amount of the
radiating conductor and the capacitor conductor, the area of the capacitor
conductor being not larger than that of the radiating conductor.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to chip antennas, antenna devices, and mobile
communication apparatus and more particularly to chip antennas, which are
compact, flat-shaped antennas that may be used favorably in mobile
communication apparatus, such as portable telephones, GPS (Global
Positioning System) receivers, etc., and antenna devices and mobile
communication apparatus.
2. Description of the Related Art
In recent years, compact size and light weight have come to be increasingly
demanded of portable telephones, GPS receivers, and other mobile
communication apparatus, and compact size is thus being demanded of parts
used in such equipment. Since the antenna is a relatively large part among
such component parts, compact size is being demanded of antennas in
particular.
Given such circumstances, flat antennas, represented by microstrip antennas
and one-side shorted microstrip antennas, have come to be developed as
small antennas in accompaniment with the advancement of mobile
communication apparatus. Among such antennas, the inverted F antenna 80,
shown in FIG. 16, uses a dielectric ceramic substrate and is known as an
antenna with which significant compactness can be achieved. The inverted F
antenna 80 is provided with a substrate 81, made of a dielectric ceramic
having magnesium oxide, calcium oxide, and titanium oxide as the main
components thereof and with a relative dielectric constant of 20. Here,
inverted F antenna 80 has a shape for example of 13.0 mm length.times.13.0
mm width.times.6.0 mm height. Metal conducting films of copper are
deposited onto the upper and lower surfaces of substrate 81 respectively
to form a radiating conductor 82 and a grounding conductor 83. A shorting
conductor 84, which is of predetermined width and is made of a metal
conducting film of copper that shorts radiating conductor 82 and grounding
conductor 83, is formed by deposition on the side surface of ceramic
substrate 81. Also in order to feed to this inverted F antenna 80, a feed
conductor 85 is provided so as to extend from a prescribed position of
radiating conductor 82 and along the side face of substrate 81. In using
such an inverted F antenna 80, the grounding conductor 83 at the lower
surface of substrate 81 is set to contact for example the metal chassis of
a portable telephone so as to use the antenna as a receiving-only antenna.
In this case, inverted F antenna 80 operates as a microstrip type inverted
F antenna. With such an inverted F antenna, the following relationship
holds for the resonance frequency f;
f=1/(2.pi..multidot.(LC).sup.1/2)
where L is the inductance component of the radiating conductor and C is the
capacitance component between the radiating conductor and the grounding
conductor, and for example, the resonance frequency in the case of
inverted F antenna 80 (FIG. 16) will be approximately 800 MHz.
However, with the conventional inverted F antenna described above, when the
resonance frequency is to be made lower to enable use down to the low
frequency range, the capacitance component between the radiating conductor
and the grounding conductor has to be made large, and for this, the
interval between the radiating conductor and the grounding conductor had
to be made extremely narrow, thus presenting the problem of requiring
precision in manufacture.
Also due to restrictions in the precision of manufacture of the interval
between the radiating conductor and the grounding conductor, a limit was
placed on the capacitance component between the radiating conductor and
the grounding conductor, thus giving rise to the problem of the range of
variation of the resonance frequency being narrow.
SUMMARY OF THE INVENTION
To overcome the above described problems, the preferred embodiments of the
present invention provide a compact chip antenna, antenna device, and
mobile communication apparatus with which the resonance frequency can be
adjusted readily and with which a wide bandwidth can be achieved.
One preferred embodiment of the present invention provides a chip antenna,
comprising: a substrate made by laminating a plurality of sheet layers
made of ceramic;
a radiating conductor having substantially planar shape and provided on
said substrate; grounding conductor having substantially planar shape and
provided so as to oppose said radiating conductor with said sheet layers
interposed in between; a capacitor conductor having substantially planar
shape and provided so as to oppose said radiating conductor and said
grounding conductor with said sheet layers interposed in between; a first
shorting conductor which connects said radiating conductor and said
grounding conductor; a second shorting conductor which connects said
grounding conductor and said capacitor conductor; a feed terminal
connected to said radiating conductor or said capacitor conductor; and a
ground terminal connected to said grounding conductor.
According to the above described chip antenna, since a capacitor conductor
having substantially planar shape is provided so as to oppose a radiating
conductor with sheet layers, that comprise a substrate, interposed in
between, the capacitance value of the capacitance component of the chip
antenna may be adjusted readily in the design stage by adjusting the
interval between the radiating conductor and the capacitor conductor or by
adjusting the area of the capacitor conductor. The resonance frequency of
the chip antenna can thus be adjusted readily in the design stage and the
deviation of the resonance frequency from the design value can be
prevented.
Also since the capacitor conductor has substantially planar shape, the area
thereof can be varied greatly. Since the capacitance value of the
capacitance component of the chip antenna can thus be varied greatly, the
variable range of the resonance frequency of the chip antenna can be made
wide.
Furthermore by adjusting the inductance component of a first shorting
conductor, which connects the radiating conductor and the grounding
conductor, just the inductance value of the inductance component can be
adjusted without varying the resonance frequency of the chip antenna.
Impedance matching of the chip antenna with an external circuit can thus
be performed readily.
In the above chip antenna, a plurality of the radiating conductors may be
=provided and at least one of the above described radiating conductors may
be fed.
According to the above described structure and arrangement, a strong
electric field is generated near the radiating conductor which is fed and
an electric current can be made to flow by means of this electric field to
the unfed radiating conductors.
Thus by the current that flows to the unfed radiating conductors, the
radiating conductor that is fed and the unfed radiating conductors are
made to resonate simultaneously. Since the chip antenna can thus be
provided with a plurality of resonance frequencies just by feeding to at
least one radiating conductor, the chip antenna can be provided with a
plurality of resonance frequencies and with a wide band.
The preferred embodiment of the present invention also provides an antenna
device comprising an above-described chip antenna and a mounting circuit
board, provided with a protruding part that extends from the end part
thereof, and characterized in that the above-mentioned chip antenna is
mounted to one of the main surfaces of the above-mentioned protruding part
and a ground electrode is provided on the other main surface of the
above-mentioned mounting circuit board.
According to the above described antenna device, since a protruding part is
extended from the end portion of a mounting circuit board and the shape of
a ground electrode near the location at which a chip antenna is mounted is
made small, the leaky electromagnetic waves from the radiating conductor
are increased and the radiation resistance of the antenna device can thus
be made large.
Thus in the process of matching the input impedance of the antenna device
with the characteristic impedance of the mobile communication apparatus to
which the antenna device is mounted, since the inductance component L of
the first shorting conductor of the chip antenna, which is a matching
element, is made large, the Q(=k(C/L).sup.1/2) of the first shorting
conductor is made small and the bandwidth of the antenna device can thus
be made wide.
Also since the current distribution on the ground electrode of the mounting
circuit board, which comprises the antenna device, can be controlled by
providing the mounting circuit board with the protruding part, the
directivity of the antenna device can be controlled.
Furthermore since a mounting circuit board is provided that has the ground
electrode provided on the other main surface, the influence of the antenna
characteristics on a human body, etc. that approaches from the ground
electrode side can be restricted.
The preferred embodiment of the present invention also provides an antenna
device comprising an above-described chip antenna and a mounting circuit
board, having the above-mentioned chip antenna mounted on one of the main
surfaces thereof and having a ground electrode provided on the other main
surface thereof, and characterized in that the ground electrode is
provided with a gap part near the location at which the chip antenna is
mounted.
According to the above described antenna device, since the ground electrode
is provided with a gap part and the shape of the ground electrode near the
location at which the chip antenna is thereby made small, the leaky
electromagnetic waves from the radiating conductor are increased and the
radiation resistance of the antenna device can thus be made large.
Thus in the process of matching the input impedance of the antenna device
with the characteristic impedance of the mobile communication apparatus to
which the antenna device is mounted, since the inductance component L of
the first shorting conductor of the chip antenna, which is a matching
element, is made large, the Q(=k(C/L).sup.1/2) of the first shorting
conductor is made small and the bandwidth of the antenna device can thus
be made wide.
Also since the current distribution on the ground electrode of the mounting
circuit board, which comprises the antenna device, can be controlled by
providing the ground electrode of the mounting circuit board with a gap
part, the directivity of the antenna device may be controlled.
Furthermore since a mounting circuit board is provided that has the ground
electrode provided on the other main surface, the influence of the antenna
characteristics on a human body, etc. that approaches from the ground
electrode side can be restricted.
The preferred embodiment of the present invention also provides a mobile
communication apparatus characterized in that an above-described antenna
device is used.
According to the above described mobile communication apparatus, since an
antenna device equipped with a wide bandwidth or an antenna device with
which the directivity can be controlled is used, wide bandwidths and
control of directivity can be realized in mobile communication apparatus.
Other features and advantages of the present invention will become apparent
from the following description of the invention which refers to the
accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view of the first preferred embodiment of the chip
antenna of the present invention.
FIG. 2 is an exploded perspective view of the substrate that comprises the
chip antenna of FIG. 1.
FIG. 3 is a perspective view of a modification of the chip antenna of FIG.
1.
FIG. 4 is a perspective view of another modification of the chip antenna of
FIG. 1.
FIG. 5 is a perspective view of yet another modification of the chip
antenna of FIG. 1.
FIG. 6A is a circuit diagram of an equivalent circuit of the chip antennas
of FIGS. 1 and 4, and FIG. 6B is a circuit diagram of an equivalent
circuit of the chip antennas of FIGS. 3 and 5.
FIG. 7 is a graph showing the variation of the resonance frequency of the
chip antenna of FIG. 1.
FIG. 8 is a perspective view of the second preferred embodiment of the chip
antenna of the present invention.
FIG. 9 is an exploded perspective view of the substrate that comprises the
chip antenna of FIG. 8.
FIG. 10 is a graph that shows the resonance frequencies of the chip antenna
of FIG. 8.
FIG. 11 is a perspective bottom view of the first preferred embodiment of
the antenna device of the present invention.
FIG. 12 is a perspective bottom view of the second preferred embodiment of
the antenna device of the present invention.
FIG. 13 is a perspective bottom view of the third preferred embodiment of
the antenna device of the present invention.
FIGS. 14A and 16B are a partially perspective bottom view of the current
distribution on the ground electrode of the substrate that comprises the
antenna device.
FIG. 15A is a perspective bottom view of a modification of the antenna
device of FIG. 12 and
FIG. 15B is a perspective bottom view of another modification of the
antenna device of FIG. 12.
FIG. 16 is a perspective view of a conventional, inverted F antenna.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a perspective view of a first preferred embodiment of the chip
antenna of the present invention. A chip antenna 10 is comprised of a
substrate 11 of rectangular parallelepiped shape, a planar radiating
conductor 12, which is provided on one of the main surfaces of substrate
11, a planar grounding conductor 13, which is provided on the other main
surface side at the interior of substrate 11 so as to oppose radiating
conductor 12, a planar capacitor conductor 14, which is provided between
radiating conductor 12 and grounding conductor 13 so as to oppose
radiating conductor 12, first shorting conductors 15, which are provided
in the interior of substrate 11 to connect radiating conductor 12 and
grounding conductor 13, second shorting conductors 16, which are provided
in the interior of substrate 11 to connect grounding conductor 13 and
capacitor conductor 14, a feed terminal T1, which is provided from the
side surface of substrate 11 to the other main surface and is connected to
radiating conductor 12 via a connecting conductor 17 that is provided in
the interior of substrate 11 and a ground terminal T2, which is provided
from the side surface of substrate 11 to the other main surface and is
connected to grounding conductor 13 at the side surface of substrate 11.
FIG. 2 is an exploded perspective view of substrate 11 that comprises chip
antenna 10 of FIG. 1. A substrate 11 is formed by laminating rectangular
sheet layers 111 to 115, made of a dielectric ceramic having barium oxide,
aluminum oxide, and silica as the main components thereof. Among these
sheet layers, sheet layer 111 has a planar radiating conductor 12, formed
from copper or copper alloy and having a substantially rectangular shape,
provided over nearly its entire surface by screen printing, vapor
deposition, or plating.
Also near one end portion of the short edge side of sheet layer 113, a
planar capacitor conductor 14, formed from copper or copper alloy and
having a substantially rectangular shape, is provided by screen printing,
vapor deposition, or plating. Furthermore, sheet layer 115 has a planar
grounding conductor 13, formed from copper or copper alloy and having a
substantially rectangular shape, provided over nearly its entire surface
by screen printing, vapor deposition, or plating, and portions of
grounding conductor 13 are drawn out towards both end parts of the long
edge side of sheet layer 115.
Also at prescribed positions of sheet layers 111 to 114, via holes VH11,
that connect the radiating conductor 12 on sheet layer 111 and the
grounding conductor 13 on sheet layer 115, are provided in the thickness
direction. These via holes VH11 become the first shorting conductors 15,
shown in FIG. 1, for connecting radiating conductor 12 and grounding
conductor 13.
Furthermore at prescribed positions of sheet layers 113 and 114, via holes
VH12, that connect the capacitor conductor 14 on sheet layer 113 and the
grounding conductor 13 on sheet layer 115, are provided in the thickness
direction. These via holes VH12 become the second shorting conductors 16,
shown in FIG. 1, for connecting grounding conductor 13 and capacitor
conductor 14.
Also at prescribed positions of sheet layers 111 to 115, via holes VH13,
that connect the radiating conductor 12 on sheet layer 111 and a feed
terminal (not shown), which is provided from the side surface of substrate
11 to the other main surface, are provided in the thickness direction.
These via holes VH13 become the connecting conductor 17, shown in FIG. 1,
for connecting radiating conductor 12 and feed terminal T1.
And by laminating sheet layers 111 to 115 and sintering, a substrate 11 is
formed that is provided on one main surface or in the interior thereof
with radiating conductor 12, grounding conductor 13, capacitor conductor
14, first shorting conductors 15, second shorting conductors 16, and
connecting conductor 17.
FIGS. 3 to 5 are perspective views of modifications of chip antenna 10. A
chip antenna 10a of FIG. 3 is comprised of a substrate 11a of rectangular
parallelepiped shape, a planar radiating conductor 12a, which is provided
on one of the main surfaces of substrate 11a, a planar grounding conductor
13a, which is provided on the other main surface side at the interior of
substrate 11a so as to oppose radiating conductor 12a, a planar capacitor
conductor 14a, which is provided between radiating conductor 12a and
grounding conductor 13a so as to oppose radiating conductor 12a, first
shorting conductors 15a, which are provided in the interior of substrate
11a to connect radiating conductor 12a and grounding conductor 13a, second
shorting conductors 16a, which are provided in the interior of substrate
11a to connect grounding conductor 13a and capacitor conductor 14a, a feed
terminal T1a, which is provided from the side surface of substrate 11a to
the other main surface and is connected to radiating conductor 12a via a
connecting conductor 17a that is provided in the interior of substrate
11a, and a ground terminal T2a, which is provided from the side surface of
substrate 11a to the other main surface and is connected to grounding
conductor 13a at the side surface of substrate 11a.
Chip antenna 10b of FIG. 4 is comprised of a substrate 11b of rectangular
parallelepiped shape, a planar capacitor conductor 14b, which is provided
on one of the main surfaces of substrate 11b, a planar grounding conductor
13b, which is provided on the other main surface side at the interior of
substrate 11b so as to oppose capacitor conductor 14b, a planar radiating
conductor 12b, which is provided between grounding conductor 13b and
capacitor conductor 14b so as to oppose capacitor conductor 14b, first
shorting conductors 15b, which are provided in the interior of substrate
11b to connect radiating conductor 12b and grounding conductor 13b, second
shorting conductors 16b, which are provided in the interior of substrate
11b to connect grounding conductor 13b and capacitor conductor 14b, a feed
terminal T1b, which is provided from the side surface of substrate 11b to
the other main surface and is connected to radiating conductor 12b via a
connecting conductor 17b that is provided in the interior of substrate
11b, and a ground terminal T2b, which is provided from the side surface of
substrate 11b to the other main surface and is connected to grounding
conductor 13b at the side surface of substrate 11b.
A chip antenna 10c of FIG. 5 is comprised of a substrate 11c of rectangular
parallelepiped shape, a planar capacitor conductor 14c, which is provided
on one of the main surfaces of substrate 11c, a planar grounding conductor
13c, which is provided on the other main surface side at the interior of
substrate 11c so as to oppose capacitor conductor 14c, a planar radiating
conductor 12c, which is provided between grounding conductor 13c and
capacitor conductor 14c so as to oppose capacitor conductor 14c, first
shorting conductors 15c, which are provided in the interior of substrate
11c to connect radiating conductor 12c and grounding conductor 13c, second
shorting conductors 16c, which is provided in the interior of substrate
11c to connect grounding conductor 13c and capacitor conductor 14c, a feed
terminal T1c, which is provided from the side surface of substrate 11c to
the other main surface and is connected to radiating conductor 12c via a
connecting conductor 17c that is provided in the interior of substrate
11c, and a ground terminal T2c, which is provided from the side surface of
substrate 11c to the other main surface and is connected to grounding
conductor 13c at the side surface of substrate 11c.
In particular with the chip antennas 10b and 10c of FIGS. 4 and 5, since
each of the capacitor conductors 14b and 14c is provided on one of the
main surfaces of the corresponding substrate 11b or 11c, the trimming of
capacitor conductor 14 is made easy and the area of capacitor conductor 14
can thus be adjusted more readily.
FIGS. 6A and 6B show equivalent circuits of chip antennas 10 and 10a to 10c
of FIG. 1 and FIGS. 3 to 5. Each of the equivalent circuits of chip
antennas 10 and 10a to 10c is comprised of an inductance component L and
capacitance components C1 and C2, with each inductance component L being
comprised of the corresponding inductance components of radiating
conductor 12, 12a, 12b, or 12c and first shorting conductors 15, i5a, 15b,
or 15c, each capacitance component C1 being comprised of the corresponding
floating capacitance across radiating conductor 12, 12a, 12b, or 12c and
grounding conductor 13, 13a, 13b, or 13c, and each capacitance component
C2 being comprised of the corresponding electrostatic capacitance across
radiating conductor 12, 12a, 12b, or 12c and capacitor conductor 14, 14a,
14b, or 14c.
With chip antennas 10 and 10b, since feed terminal T1 is connected to the
corresponding radiating conductor 12 or 12b via connecting conductor 17 or
17b, the capacitance component C2, which is comprised of the corresponding
electrostatic capacitance across radiating conductor 12 or 12b and
capacitor conductor 14 or 14b, is formed between the inductance component
L, comprised of the corresponding inductance components of radiating
conductor 12a or 12c and first shorting conductors 15a or 15c, and the
ground as shown in FIG. 6A.
Meanwhile with chip antennas 10a and 10c, since feed terminal T1 is
connected to the corresponding capacitor conductor 14a or 14c via
grounding conductor 17a or 17c, the capacitance component C2, which is
comprised of the corresponding electrostatic capacitance across radiating
conductor 12a or 12c and capacitor conductor 14a or 14c, is formed between
the inductance component L, comprised of the corresponding inductance
components of radiating conductor 12a or 12c and first shorting conductors
15a or 15c, and the feed source V as shown in FIG. 6B.
The above-described equivalent circuits (FIGS. 6A and 6B) show that since
the capacitance values of capacitance components C2 of chip antennas 10
and 10a to 10c may be adjusted readily by adjusting the area of the
corresponding capacitor conductors 14 and 14a to 14c, the resonance
frequencies of chip antennas 10 and 10a to 10c can be adjusted readily.
It can also be understood that since the inductance values of inductance
components L of chip antennas 10 and 10a to 10c can be adjusted readily by
adjusting the inductance component of the corresponding first shorting
conductors 15 and 15a to 15c, impedance matching with an external circuit,
such as the high-frequency unit, etc., of mobile communication apparatus
having chip antenna 10, 10a, 10b, or 10c mounted therein, may be achieved
readily.
The above points shall now be explained by way of an actually manufactured
chip antenna of 5.0 mm length.times.15.0 mm width.times.3.0 mm height.
FIG. 7 is a graph that shows the variation of the resonance frequency of
chip antenna 10. This graph shows the results of investigation of the
relationship between the area of capacitor conductor 14 and the resonance
frequency of chip antenna 10. This graph shows that as the area of
capacitor conductor 14 is made smaller, that is, as the capacitance value
of capacitance component C2 of chip antenna 10 is made smaller, the
resonance frequency of chip antenna 10 is made higher.
This shows that the resonance frequency of chip antenna 10 may be adjusted
readily by adjusting the area of capacitor conductor 14. It also shows
that the resonance frequency of chip antenna 10 can be adjusted readily by
adjusting the area of capacitor conductor 14 by trimming capacitor
conductor 14 with a laser, etc.
It can also be understood that the VSWR (Voltage Standing Wave Ratio) at
the resonance frequency of chip antenna 10 is 1.2 or less and thus that
good antenna characteristics are exhibited. This shows that the adjustment
of the area of capacitor conductor 14 for the adjustment of the resonance
frequency of chip antenna 10 does not have an influence on the antenna
characteristics of chip antenna.
The variation of the characteristic impedance of chip antenna 10 is shown
in Table 1. This Table shows the results of investigation of the
relationship between the number of shorting conductors 14 that have been
disconnected and the characteristic impedance of chip antenna 10.
TABLE 1
______________________________________
Number of first shorting
Resonance
conductors that have
frequency Characteristic impedance Z(.OMEGA.)
been disconnected
(GHz) R X
______________________________________
0 1.94 15.6 38.0
1 1.94 35.4 41.3
2 1.93 54.1 26.4
3 1.93 53.2 2.35
______________________________________
*The characteristic impedance is given by Z = R + iX (.OMEGA.).
The above Table shows that as the number of disconnected first shorting
conductors 15, that connect radiating conductor 12 and grounding conductor
13, is increased, that is, as the inductance component of first shorting
conductors 15, which comprises inductance component L (FIG. 6) of chip
antenna 10, is increased, the conditions R=50 and X=0 are approached for
the characteristic impedance (Z=R+iX) of chip antenna 10, that is, the
characteristic impedance Z is brought closer to 50 (.OMEGA.). In this
process, the resonance frequency of chip antenna 10 hardly varies.
Since the characteristic impedance of a high-frequency unit or other
external circuit of mobile communication apparatus equipped with chip
antenna 10 is generally 50(.OMEGA.), impedance matching of the chip
antenna with the external circuit can be achieved by bringing the
characteristic impedance of the chip antenna close to 50. This shows that
impedance matching of chip antenna 10 with an external circuit may be
achieved readily by adjusting the inductance value of inductance component
L of chip antenna 10.
As has been described above, with the chip antenna of the first embodiment,
since a substantially planar capacitor conductor is provided so as to
oppose the radiating conductor with sheet layers, that comprise the
substrate, interposed in between, the capacitance value of the capacitance
component of the chip antenna may be adjusted readily by adjusting the
interval between the radiating conductor and the capacitor conductor or
the area of the capacitor conductor. The resonance frequency of the chip
antenna can thus be adjusted readily by adjusting the interval between the
radiating conductor and the capacitor conductor or the area of the
capacitor conductor.
Since the interval between the radiating conductor and the capacitor
conductor may be adjusted readily by varying the thickness of the sheet
layers provided between the radiating conductor and the capacitor
conductor, interval can be determined at the design stage. The area of the
capacitor conductor can also be determined at the design stage. The
determination of the capacitance value of the capacitance component of the
chip antenna at the design stage, which was not possible with the
conventional inverted F antenna, is thus made possible and the deviation
of the resonance frequency of the chip antenna from the design value can
be prevented.
Also since the capacitor conductor is substantially planar, its area can be
varied greatly. Since the capacitance value of the capacitance component
of the chip antenna can thus be varied greatly, the range of variation of
the resonance frequency of the chip antenna can be widened.
Furthermore by adjusting the inductance component of the first shorting
conductors that connect the radiating conductor and the grounding
conductor, just the inductance value of the inductance component can be
adjusted without varying the resonance frequency of the chip antenna.
Impedance matching of the chip antenna with an external circuit can thus
be achieved readily.
FIG. 8 is a perspective view of a second preferred embodiment of the chip
antenna by the present invention. Chip antenna 20 is comprised of a
substrate 21 of rectangular parallelepiped shape, two planar radiating
conductors 22a and 22b, which are provided on one of the main surfaces of
substrate 21, a planar grounding conductor 23, which is provided on the
other main surface side at the interior of substrate 11 so as to oppose
radiating conductors 22a and 22b, two planar capacitor conductors 24a and
24b, which are provided between radiating conductors 22a and 22b and
grounding conductor 23 so as to oppose radiating conductors 22a and 22b,
respectively, first shorting conductors 25a and 25b, which are provided in
the interior of substrate 21 to connect radiating conductors 22a and 22b
and grounding conductor 23, second shorting conductors 26a and 26b, which
are provided in the interior of substrate 21 to connect grounding
conductor 23 and capacitor conductors 24a and 24b, a feed terminal Ti,
which is provided from the side surface of substrate 21 to the other main
surface and is connected to just one radiating conductor 22a via a
connecting conductor 27 that is provided in the interior of substrate 21,
and a ground terminal T2c, which is provided from the side surface of
substrate 21 to the other main surface and is connected to grounding
conductor 23 at the side surface of substrate 21.
FIG. 9 is an exploded perspective view of substrate 21 that comprises chip
antenna 20 of FIG. 8. A substrate 21 is made by laminating rectangular
sheet layers 211 to 215, made of a dielectric ceramic having barium oxide,
aluminum oxide, and silica as the main components thereof. Among these
sheet layers, sheet layer 211 has two planar radiating conductors 22a and
22b, formed from copper or copper alloy and having a substantially
rectangular shape, provided near the respective end portions of the long
edge side by screen printing, vapor deposition, or plating.
Also near one end portion of the short edge side of sheet layer 213, two
planar capacitor conductors 24a and 24b, formed from copper or copper
alloy and having a substantially rectangular shape, are provided by screen
printing, vapor deposition, or plating. Furthermore, sheet layer 215 has a
planar grounding conductor 23, formed from copper or copper alloy and
having a substantially rectangular shape, provided over nearly its entire
surface by screen printing, vapor deposition, or plating, and portions of
grounding conductor 23 are drawn out towards both end parts of the long
edge side of sheet layer 215.
Also at prescribed positions of sheet layers 212 to 215, via holes VH21a
and VH21b, that connect the radiating conductors 22a and 22b on sheet
layer 215 and the grounding conductor 23 on sheet layer 215, are provided
in the thickness direction. These via holes VH21a and VH21b become the
first shorting conductors 25a and 25b, shown in FIG. 8, for connecting
radiating conductors 22a and 22b and grounding conductor 23.
Furthermore at prescribed positions of sheet layers 213 and 214, via holes
VH22a and VH22b, that connect the capacitor conductors 24a and 24b on
sheet layer 213 and the grounding conductor 23 on sheet layer 215, are
provided in the thickness direction. These via holes VH22a and VH22b
become the second shorting conductors 26a and 26b, shown in FIG. 8, for
connecting grounding conductor 23 and capacitor conductors 24a and 24b.
Also at prescribed positions of sheet layers 211 to 215, via holes VH23,
that connect one radiating conductor 22a on sheet layer 211 and a feed
terminal (not shown), which is provided from the side surface of substrate
21 to the other main surface, are provided in the thickness direction.
These via holes VH23 become the connecting conductor 27, shown in FIG. 8,
for connecting radiating conductor 22 and feed terminal T1.
And by laminating sheet layers 211 to 215 and sintering, a substrate 21 is
formed that is provided on one main surface or in the interior thereof
with two radiating conductors 22a and 22b, grounding conductor 23, two
capacitor conductors 24a and 24b, first shorting conductors 25a and 25b,
and second shorting conductors 26a and 26b.
FIG. 10 is a graph that shows the frequency characteristics of chip antenna
20. In FIG. 10, the solid line indicates the characteristics of chip
antenna 20 (FIG. 8) and the broken line indicates the characteristics of
chip antenna 10 (FIG. 1) for comparison. This diagram shows that chip
antenna 20 has two resonance frequencies and a wider bandwidth in
comparison to chip antenna 10. For example, a comparison of the bandwidths
for VSWR<3 show that whereas the bandwidth is approximately 113.9 MHz with
chip antenna 10 (FIG. 1), the bandwidth is approximately 209.8 MHz or
approximately 85(%) wider with chip antenna 20 (FIG. 8).
Furthermore it can be understood that, as with chip antenna 10, good
antenna characteristics are exhibited, with the VSWR at the resonance
frequency being 1.2 or less.
As has been described above, with the chip antenna of the second preferred
embodiment, by providing two radiating conductors and connecting only one
of the radiating conductors to the feed terminal so that just one of the
radiating conductors is fed, a strong electric field is generated near one
of the radiating conductors and electric current can be made to flow to
the other radiating conductor by this electric field.
As a result, the one radiating conductor and the other radiating conductor
can be made to resonate simultaneously by making current flow to the other
radiating conductor and the chip antenna may thereby be made to have a
plurality of resonance frequencies and, in accompaniment, a wide
bandwidth, just by feeding to one radiating conductor.
Also since just one of the radiating conductors is fed, the voltage
necessary for feeding may be made low.
FIG. 11 is a perspective bottom view of a first preferred embodiment of the
antenna device by the present invention. Antenna device 30 is comprised of
the antenna device 10 of FIG. 1 or the antenna device 20 of FIG. 8 and a
mounting circuit board 32 from which a protruding part 31 is extended from
its end portion. On one of the main surfaces of protruding part 31, in
other words, on the same surface as one of the main surfaces of mounting
circuit board 32 is mounted chip antenna 10, and on the other main surface
of mounting circuit board 32 is provided a ground electrode 33.
FIG. 12 is a perspective bottom view of a second preferred embodiment of
the antenna device by the present invention. Antenna device 40 is
comprised of the antenna device 10 of FIG. 1 or the antenna device 20 of
FIG. 8 and a mounting circuit board 42, having a chip antenna 10 mounted
to one main surface and a ground electrode 41 provided on the other main
surface. The ground electrode 41 that is provided on the other main
surface of mounting circuit board 42 has a substantially L-shaped gap part
43, which is a portion at which ground electrode 41 is not provided, near
the location where chip antenna 10 is mounted.
FIG. 13 is a perspective bottom view of a third preferred embodiment of the
antenna device by the present invention. Antenna device 50 is comprised of
the antenna device 10 of FIG. 1 or the antenna device 20 of FIG. 8 and a
mounting circuit board 52, having a chip antenna 10 mounted to one main
surface and a ground electrode 51 provided on the other main surface. The
ground electrode 51 that is provided on the other main surface of mounting
circuit board 52 has a wide, substantially rectangular gap part 53 near
the location at which chip antenna 10 is mounted. That is, in comparison
to antenna device 40 of the second embodiment, the area of gap part 53,
which is provided to ground electrode 51 that is provided on the other
main surface of mounting circuit board 52, is made greater.
Table 2 shows the bandwidths of antenna devices 30 to 50 of the
above-described first to third preferred embodiments for the case where
chip antenna 10 of FIG. 1 is used. In Table 2, the comparative example is
a device in which chip antenna 10 of FIG. 1 is mounted on a rectangular
mounting circuit board provided with a ground electrode over the entire
surface of the other main surface thereof.
TABLE 2
______________________________________
Antenna Antenna Antenna Comparative
device 30 device 40 device 50 Example
______________________________________
Bandwidth
123.0 121.0 92.0 70.1
(MHz)
______________________________________
*The bandwidth is the frequency range in which the VSWR (Voltage Standing
Wave Ratio) is 3 or less.
These results show that as the shape of the ground electrode near the
location at which the chip antenna is mounted is made smaller, that is, as
the ground electrode smaller, the bandwidth of the antenna device is made
wider.
That is, the bandwidth becomes wider in the order of the comparative
example, antenna device 40, in which a substantially L-shaped gap part is
provided near the location at which the chip antenna is mounted, antenna
device 50, in which a wide, substantially rectangular gap part is provided
near the location at which the chip antenna is mounted, and antenna device
30, in which a protruding part is provided at the end portion of the
mounting circuit board and the chip antenna is mounted to this protruding
part.
Table 3 shows the bandwidths of antenna devices 30 to 50 of the
above-described first to third preferred embodiments for the case where
chip antenna 20 of FIG. 8 is used. In Table 3, the comparative example is
a device in which chip antenna 30 of FIG. 8 is mounted onto a rectangular
mounting circuit board provided with a ground electrode over the entire
surface of the other main surface thereof.
TABLE 3
______________________________________
Antenna Antenna Antenna Comparative
device 30 device 40 device 50 Example
______________________________________
Bandwidth
162.3 159.3 137.4 107.2
(MHz)
______________________________________
*The bandwidth is the frequency range in which the VSWR (Voltage Standing
Wave Ratio) is 3 or less.
These results also show that as the shape of the ground electrode near the
location at which the chip antenna is mounted is made smaller, the
bandwidth of the antenna device is made wider.
That is, the bandwidth becomes wider in the order of the comparative
example, antenna device 40, in which a substantially L-shaped gap part is
provided near the location at which the chip antenna is mounted, antenna
device 50, in which a wide, substantially rectangular gap part is provided
near the location at which the chip antenna is mounted, and antenna device
30, in which a protruding part is provided at the end portion of the
mounting circuit bard and the chip antenna is mounted to this protruding
part.
The reason for the above may be explained as follows. That is, by extending
a protruding part from the end portion of the mounting circuit board or by
providing a gap part in the ground electrode, the shape of the ground
electrode near the location at which the chip antenna is mounted is made
smaller.
Since the leaky electromagnetic waves from the radiating conductor are thus
increased and the radiation resistance of the antenna device is made
greater, the inductance component L of the first shorting conductors of
the chip antenna, which comprise a matching element, must be made greater
in order to match the input impedance of the antenna device with the
characteristic impedance of the mobile communication apparatus to which
the antenna device is mounted.
As a result, the Q(=k(C/L).sup.1/2) of the first shorting conductors is
made smaller and since the frequency characteristics are thus widened, an
antenna device comprising a chip antenna provided with first shorting
conductors of small Q is made wide in bandwidth.
Table 4 shows the bandwidths for cases where the length direction dimension
a and width direction dimension b of the substantially L-shaped gap part
are varied in the above-described antenna device 40 of the second
embodiment.
TABLE 4
______________________________________
V [mm] 0 6 12 18 18 18
W [mm] 0 0 0 0 2 4
Bandwidth (MHz)
76.4 78.8 80.6 86.6 89.5 92.0
______________________________________
These results show that as the size of the gap part is made greater and the
shape of the ground electrode near the location at which the chip antenna
is mounted is made smaller, the bandwidth of the antenna device is made
wider. The reason for this is the same as that explained above for the
cases of Tables 2 and 3.
FIG. 14 is a partially perspective bottom view of the current distribution
on the ground electrode of a mounting circuit board that comprises an
antenna device. FIG. 14A shows the current distribution for the case where
the V and W of gap part 43 of ground electrode 41 in the antenna device 40
of FIG. 12 are set to 22 mm and 2 mm, respectively, and FIG. 14B shows the
current distribution for the comparative case where ground electrode 41 is
not provided with gap part 43, that is, for the case of a solid electrode.
In FIGS. 14A and 14B, the directions of the arrows indicate the directions
of the current and the lengths of the arrows indicate the magnitudes of
the current.
These results show that whereas in the case where ground electrode 41 is
not provided with a gap part 43 (FIG. 14B) the current is distributed
nearly parallel to the length direction of chip antenna 10 or 20, in the
case where ground electrode 41 is provided with gap part 43 (FIG. 14A),
the current is distributed nearly perpendicular to the length direction of
chip antenna 10 or 20 at the location at the side of gap part 43 opposite
the mounting position of chip antenna 10 or 20.
This shows that the current distribution on ground electrode 41 of mounting
circuit board 42, which comprises antenna device 40, is changed by the
provision of ground electrode 41 with gap part 43.
This therefore shows that by providing ground electrode 41 with gap part
43, the current distribution on ground electrode 41 of mounting circuit
board 42, which comprises antenna device 40, can be controlled and thus
the directivity of antenna device 40 can be controlled. With the antenna
device of FIG. 14A, a measurement of the directivity of the antenna device
showed that the polarized wave in the direction perpendicular to the
length direction of chip antenna 10 or 20 was strong and the polarized
wave in the parallel direction was weak.
The control of the current distribution on the ground electrode of the
mounting circuit board that comprises the antenna device may be carried
out in likewise manner in the antenna device 30 of FIG. 11 which is
provided with a protruding part and in the antenna device 50 of FIG. 13 in
which a wide, substantially rectangular gap part is provided. The
directivity may thus be controlled in likewise manner in antenna devices
30 and 50.
With the antenna devices of the first to third embodiments described above,
since the shape of the ground electrode near the location at which the
chip antenna is mounted is made smaller by extending a protruding part
from the end portion of the mounting circuit board or by providing the
ground electrode with a gap part, the leaky electromagnetic waves from the
radiating conductor are increased, and as a result, the radiation
resistance of the antenna device can be made greater.
Thus in the process of matching the input impedance of the antenna device
with the characteristic impedance of the mobile communication apparatus to
which the antenna device is mounted, since the inductance component L of
the first shorting conductor of the chip antenna, which is a matching
element, is made large, the Q(=k(C/L).sup.1/2) of the first shorting
conductor is made small and the bandwidth of the antenna device can thus
be made wide. As a result, a wide bandwidth can be realized in mobile
communication apparatus equipped with this antenna device.
Also since the current distribution on the ground electrode of the mounting
circuit board, which comprises the antenna device, can be controlled by
providing the mounting circuit board with a protruding part or by
providing the ground electrode of the mounting circuit board with a gap
part, the directivity of the antenna device can be controlled. Control of
directivity can thus be realized in mobile communication apparatus
equipped with this antenna device.
Furthermore since a mounting circuit board having a ground electrode
provided on the other main surface is provided, the influence of the
antenna characteristics on a human body, etc. that approaches from the
ground electrode side can be restricted.
Although cases in which the substrate is comprised of a dielectric ceramic
having barium oxide, aluminum oxide, and silica as the main components
thereof were described with the chip antennas of the first and second
preferred embodiments, the substrate is not limited to being a dielectric
ceramic and may be a dielectric ceramic having titanium oxide and
neodymium oxide as the main components thereof, a magnetic ceramic having
nickel, cobalt, and iron as the main components thereof, or a combination
of a dielectric ceramic and a magnetic ceramic.
Also, although cases in which the radiating conductor, capacitor conductor,
and grounding conductor have a substantially rectangular shape were
described, this shape is not limited thereto and the same effects may be
obtained with a substantially circular shape, substantially elliptical
shape, or polygonal shape, etc. as long as the shape is planar.
Furthermore, although cases in which one of either the radiating conductor
or the capacitor conductor is provided in the interior of the substrate
were described, the same effects may be obtained in cases where both the
radiating conductor and the capacitor conductor are provided in the
interior of the substrate.
Also, although cases in which the grounding conductor is provided in the
interior of the substrate were described, the same effects may be obtained
in cases where the grounding conductor is provided on the other main
surface of the substrate.
Furthermore, although cases in which the first and second shorting
conductors are provided in the interior of the substrate were described,
the same effects may be obtained in cases where these conductors are
provided on a main surface or side surface of the substrate.
Also, although the case in which the feed terminal is connected to the
radiating conductor was described with the chip antenna of the second
preferred embodiment, the same effects may be obtained in cases where the
feed terminal is connected to the capacitor conductor as in a modification
of the first preferred embodiment.
Furthermore, although the case in which two radiating conductors are
provided on one main surface of the substrate was described, a plurality
of radiating conductors may be equipped and since as the number of
radiating conductors is increased, the number of resonance frequencies can
be increased in accordance with the number of radiating conductors, a chip
antenna with a wider bandwidth may be realized.
Also, although a wide bandwidth may be realized by feeding to the plurality
of radiating conductors, the voltage necessary for feeding may be lowered
more significantly if the number of radiating electrodes that are fed is
made fewer.
Furthermore, although the case where the shape of the gap part is
substantially an L-shape, which is bent in the direction in which the chip
antenna is not mounted, was described with the antenna device of the
second embodiment, the same effects may be obtained if the shape of gap
part 43a or 43b is substantially an L-shape (FIG. 15(a)) or substantially
a J-shape (FIG. 15(b)) that is bent in the direction in which chip antenna
10 is mounted.
While the invention has been particularly shown and described with
reference to preferred embodiments thereof, it will be understood by those
skilled in the art that the forgoing and other changes in form and details
may be made therein without departing from the spirit of the invention.
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